Capacity control scroll compressor

ABSTRACT

A capacity-controlled scroll compressor for reducing a start shock and improving machinability of a fixed end plate, wherein a high pressure Ph to be guided to a control valve ( 70 ) for controlling a control pressure Pm for operating a shuttle valve ( 60 ) is introduced from a high pressure passage ( 72 ) opening at a discharge port ( 1   c ) to reduce a start shock. A bypass hole ( 52   a ) and the high pressure passage ( 72 ) are constituted by a straight through-hole extending through a cylinder ( 61 ) from the outer peripheral portion of a fixed end plate ( 1   a ) and consequently, machinability of the fixed end plate ( 1   a ) can be improved.

FIELD OF THE INVENTION

The present invention relates to a capacity control mechanism of ascroll compressor for use in automotive air conditioning apparatus.

BACKGROUND OF THE INVENTION

As a capacity-controlled type scroll compressor having a valve mechanismfor opening and closing a bypass hole, there has been a configuration asdisclosed in Japanese Laid-Open Patent Application No. Hei 4-179886, forexample, in which a bypass hole is defined on an end plate of a fixedscroll, and a capacity control block incorporating a bypass passageenabling the bypass hole to communicate with a suction chamber formedinside the housing and a valve mechanism for opening and closing thebypass passage is constituted as a unit separate from the fixed scrollso that a high pressure introduced from a discharge cavity can besupplied to a control valve for regulating the control pressure of thevalve mechanism for opening and closing the bypass hole.

As another example, there is a system as disclosed in Japanese Laid-OpenPatent Application No. Hei 5-280476, in which a cylinder is provided ina fixed scroll member, into which a plunger which is capable ofsequentially closing a group of bypass holes communicating between thecylinder and the compression chamber is inserted, and in which a highpressure to be supplied to a control valve for controlling the controlpressure for reciprocating the plunger is introduced from nearby thefront end of the innermost periphery of a vane formed on the fixedscroll.

However, in the above-described prior art configuration, as the highpressure to be supplied to the control valve is introduced from adischarge cavity, when the compressor is restarted under a state of ahigh discharge pressure, the high discharge pressure is applied to thecontrol valve and the valve mechanism causing the bypass holes closed.Consequently, the compressor is started at a maximum capacity thussuffering from a large shock. On the other hand, in the latter example,although the high pressure to be supplied to the control valve isintroduced from nearby the front end of the innermost periphery of thevane formed on the fixed scroll member, the configuration and machiningof the lead-in passage are extremely difficult.

DISCLOSURE OF THE INVENTION

In the view of the above described shortcomings of the prior art, it isan object of the present invention to provide a capacity-controlledscroll compressor in which the start shock is reduced and themachinability of the fixed end plate is improved.

In order to attain the above object, the present invention providesinside a fixed end plate a control-pressure chamber which houses acontrol valve for controlling the controlling pressure for reciprocatinga shuttle valve and a high pressure passage opening in the controlchamber for introducing a high pressure to the control valve, the otherend of the high pressure passage being open at a discharge hole, therebyrealizing reduction of the start shock of the compressor with a simplepassage structure.

Also, by forming one of the bypass holes communicating with a fluidpocket on the side wall of the discharge hole such that the bypass holecommunicates with a cylinder with a straight through-hole from the outerperipheral end of the fixed end plate, or making the cylinder, thebypass hole, and the high pressure passage communicate with a straightthrough-hole from the outer peripheral end of the fixed end plate, it ispossible to reduce the start shock of the compressor as well as toimprove the machinability of the fixed end plate.

In other words, the scroll compressor of the present invention is one inwhich a high pressure is introduced through a passage opening at adischarge hole to a control valve for controlling the control pressurefor opening and closing bypass holes with a shuttle valve.

By employing this structure, as a high pressure is instantaneouslyreduced to a low pressure immediately after a compressor operation hasstopped, the control pressure acting on a shuttle valve is also reducedto a low pressure and the shuttle valve comes to state of opening thebypass holes. As a result, when the compressor is restarted, the startshock can be reduced as the compressor is always started at a minimumcapacity. Also, the structure of the high pressure passage can be madesimpler as the control-pressure chamber and the discharge hole can bemade closer to each other.

The other embodiments of the present invention have one of the bypassholes formed on the side wall of the discharge hole and the bypass holeand the cylinder are made to communicate with a straight through-holefrom the outer peripheral end of the fixed end plate, or the cylinder,the bypass hole formed on the side wall of the discharge hole and a highpressure passage opening at the discharge hole and introducing a highpressure to the control-pressure chamber are made to communicate with astraight through-hole from the outer peripheral end of the fixed endplate.

According to this structure, it is possible to reduce the start shock aswell as to facilitate the simultaneous machining of the individualcommunicating holes and the passage of the fixed end plate therebyimproving machinability.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will be bestunderstood by reference to the accompanying drawings wherein:

FIG. 1 is a partially in phantom sectional view of a capacity-controlledscroll compressor in a preferred embodiment of the present invention.

FIG. 2 is a partially in phantom sectional view of a fixed end platethereof taken along the line 2—2 in FIG. 1.

FIG. 3 is a partially in phantom transverse sectional view of acompression chamber of the compressor taken along line 3—3 in FIG. 1.

FIG. 4 is a graphical diagram showing the relationship between theorbiting angle and the enclosed volume of the compressor.

FIG. 5 is a graphical diagram showing the relationship between theshuttle valve stroke and controlled capacity of the compressor.

FIG. 6 is a graphical diagram showing the pressure characteristics ofthe pressure control valve of the compressor of the present invention atdifferent cooling loads.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the basic construction of preferred embodiment ofthe compressor of the present invention will be described as follows:

In FIG. 1, a compressor housing 3 is divided into a front housing 31 anda rear plate 35, and includes therein a fixed scroll 1 having a fixedend plate 1 a and a spiral wrap 1 b erecting or upstanding from fixedend plate 1 a, and an orbiting scroll 2 having an orbiting end plate 2 aand a spiral wrap 2 b erecting or upstanding from orbiting end plate 2 aand engaged with fixed scroll 1 with both wraps 1 b and 2 b facinginward and intermeshed as shown. To provide an orbiting mechanism, acylindrical boss 2 c is formed on the rear side of the orbiting endplate 2 a on the opposite side of the spiral wrap 2 b of orbiting scroll2, and an orbiting bearing 7 is provided on boss 2 c. A drive shaft 9 isrotatably supported via a main bearing 15 fitted in front housing 31,and a main shaft portion 9 a projects outside of front housing 31passing through a shaft sealing device 17 and a subsidiary bearing 16. Adrive pin 9 b disposed at the end of drive shaft 9 on the orbitingscroll 2 side is coupled with an orbiting bush 8 functioning as a drivetransmission mechanism inserted in orbiting bearing 7, and gives anorbiting motion to orbiting scroll 2 by transmitting the driving forcefrom drive shaft 9. A flat plate thrust bearing 4 is provided betweenorbiting end plate 2 a and front housing 31, for directing the axiallythrust exerted on orbiting scroll 2 in parallel to orbiting end plate 2a. A motion restricting component 6 is provided for restricting themotion of an Oldham ring 5 which restricts the movement of the orbitingscroll 2 so as to permit it to only make an orbiting motion at rightangles to drive shaft 9.

An O-ring 18 is inserted in a sealing groove 1 f on the outer peripheralportion 1 e of fixed end plate 1 a of fixed scroll 1 and functions as asealing member for partitioning the interior of compressor housing 3into a high pressure chamber 11 and a low pressure chamber 12. Fixedscroll 1 and the rear plate 35 form the high pressure chamber 11. Theyare assembled by a bolt 19 through the fastening hole 1 d provided onthe rear side of fixed end plate 1 a. The high pressure chamber has adischarge port 14.

Revolution restraining component 6 is secured on a front end portion 32inside the front housing 31. The front housing 31 has a suction port 13.The orbiting scroll 2 is pressed against the revolution restrainingcomponent 6 by the thrust force via thrust bearing 4. Front housing 31is closed by rear plate 35 in the vicinity of the outer circumference offixed end plate 1 a of fixed scroll 1. A thrust clearance adjusting shim20 is interposed between the front housing 31 and the rear plate 35 toadjust thrust clearance.

As a result of the orbiting motion of orbiting scroll 2, the refrigerantis introduced from outside of compressor housing 3 into the interior lowpressure chamber 12 through suction port 13 and led to the vicinities ofthe outer peripheries of wrap 1 b and wrap 2 b of fixed scroll 1 andorbiting scroll 2, respectively. The refrigerant is then sucked into afluid pocket 10 formed by and enclosed between both wraps 1 b and 2 b byan orbiting motion of orbiting scroll 2, compressed into a smallervolume as it goes from the outer peripheries of both wraps 1 b and 2 btoward the center, and is discharged into high pressure chamber 11through a gas discharge hole 1 c in the fixed end plate 1 a. A reedvalve or discharge valve 21 is fitted on discharge hole 1 c from thehigh pressure side of chamber 11 to prevent the back flow of thedischarged gas.

Referring now to FIGS. 2 and 3, the construction of the capacitycontrolled mechanism will be described. Generally, a shuttle valve 60cooperates with a plurality of bypass holes to partially relieve thepressure in the compressor to vary its capacity and to reduce thestarting shock of the compressor using a simple bypass construction.

In fixed end plate 1 a, two pairs of bypass holes 50 a, 50 b and 51 a,51 b are provided, each pair respectively communicating with each of apair of fluid pockets 50 and 51 which are in the same compressionprocess, and a bypass hole 52 a is provided on the side wall of thedischarge hole or discharge port 1 c which communicates with the regionin which the pair of fluid pockets merge into one fluid pocket 52 as thecompression process further proceeds.

A shuttle valve 60 is slidably inserted in a cylinder cut out 61 insidefixed end plate 1 a. Shuttle valve 60 sequentially closes the bypassholes 50 a, 50 b, 51 a, 51 b and 52 a. As best shown in FIG. 3, one endof cylinder cut out 61 is open at a cut-away portion 1 g formed on theouter peripheral portion 1 e of fixed end plate 1 a and communicateswith low pressure chamber 12. Shuttle valve 60 is pushed by thecompressive force of the spring 62 in the leading end direction. Theouter end of spring 62 is retained within fixed end plate 1 a by aholder 63 and a stop ring 64.

Shuttle valve 60 has two recessed portions 60 a and 60 b on its outercylindrical surface. Recessed portion 60 a is provided at a position atwhich it communicates with bypass holes 51 a and 51 b at the timeshuttle valve 60 is in the state of being pushed in the leading enddirection (i.e., when spring 62 is extended). Similarly, recessedportion 60 b is provided at a position at which it communicates withbypass hole 52 a. Furthermore, a communicating hole 66 is drilled onrecessed portion 60 a allowing communication with low pressure chamber12 through the interior of shuttle valve 60. The third recessed portion60 b communicates with low pressure chamber 12 through a passage 67passing through fixed end plate 1 a and cut-away portion 1 h formed onouter peripheral portion 1 e of the fixed end plate.

A lead-in hole 68 is drilled at the leading end of cylinder cut out 61to allow introduction of a control pressure Pm which makes shuttle valve60 operable by overcoming the compressive or pushing force of spring 62.

On the other hand, a pressure control valve 70 for controlling thecontrol pressure Pm is incorporated in a control-pressure chamber 71inside fixed end plate 1 a. The pressure control valve 70 is held by aholder 78 and a stop ring 79.

Control-pressure chamber 71 communicates with a high pressure passage 72for taking in a high pressure Ph and a flow-out hole 73. As best shownin FIG. 1, high pressure passage 72 communicates with discharge hole 1c. Flow-out hole 73 communicates with low pressure chamber 12 via acut-away portion 1 i formed on the outer peripheral portion 1 e of fixedend plate 1 a. The flow-out hole 73 also serves as a passage for takingin suction pressure Ps as a low pressure signal. Also, a communicatinghole 74 for taking in atmospheric pressure Pa to be used as a basesignal is drilled on the rear side of fixed end plate 1 a and is open tothe air through a hole 36 drilled on an O-ring 75 and rear plate 35.

Pressure control valve 70 generates an adequate control pressure Pm inresponse to changes in the high pressure Ph and the suction pressure Ps.The control pressure Pm is transmitted to cylinder 61 through passage 76formed on the rear side of fixed end plate 1 a and the earlier-mentionedlead-in hole 68. Passage 76 is sealed by the rear plate 35 and O-ring77. In operation, one side of the pressure control valve 70 communicateswith the atmospheric pressure Pa or base pressure through communicatinghole 74. The other side communicates with suction pressure Ps throughflow-out hole 73. Thus, the control valve 70 will move responsive to thedifference between Ps and Pa. High pressure passage 72 communicatesbetween the discharge hole 1 c and the control pressure chamber 71 andthe fluid pressure in high pressure passage 72 is controlled by themovement of control valve 70. The pressure control valve 70 eitherallows the high pressure fluid to pass through the flow-out hole 73 intothe compressor housing or prevents the flow-out causing the highpressure fluid to be directed into passage 76 to supply the controlpressure Pm. Specifically, when the suction pressure Ps is higher thanthe atmospheric pressure Pa the control valve 70 moves preventing thecompressed fluid in the high pressure passage from flowing out of theflow-out hole 73 thereby increasing the control pressure Pm. Theincreased control pressure then passes through passage 76 throughlead-in hole 68 into the cylinder 61 causing shuttle valve 60 to move bycompressing spring 62 and closing bypass holes 51 a, 51 b, 50 a, 50 band 52 a.

Conversely, when the cooling load is low, the suction pressure Ps islikewise low causing the control valve 70 to move to the position shownin FIG. 3 opening the passage between the high pressure passage 72 andthe flow-out hole 73 in the control pressure chamber 71. Thus, thecontrol pressure Pm communicating with the shuttle valve 60 throughpassage 76 and lead in hole 68 is reduced enabling spring 62 to overcomethe control pressure Pm and move the shuttle valve 60 to the positionshown in FIG. 3 wherein the bypass holes 51 a, 51 b, 50 a, 50 b, and 52a are open.

Operation of the capacity control mechanism will now be described withreference to FIGS. 4 and 5.

When shuttle valve 60 is at its uppermost position (in the leading enddirection of the cylinder) (i.e., when spring 62 is extended as shown inFIG. 3), all the bypass holes are fully open and the operation will beat a minimum capacity. Conversely, when shuttle valve 60 is at itslowermost position (on the holder side) (i.e., when spring 62 iscompressed), all the bypass holes are fully closed and the operationwill be at a maximum capacity. As can be seen in FIG. 4, bypass holes 51a and 51 b communicate with the fluid pockets up to 100% to about 60% ofthe region of the maximum compressed volume Vmax. Likewise, bypass holes50 a and 50 b communicate with 100% to about 50%, and bypass hole 52 acommunicates with about 60% to about 0% of the region. By adjusting theopenings of these bypass holes with the shuttle valve, the controlledcapacity (Vc) vs. shuttle valve stroke (Ls) relationship as shown inFIG. 5 can be obtained.

In FIG. 5, the controlled capacity Vc (on the ordinate axis) representsthe percentage ratio of the enclosed volume under control to the maximumenclosed volume of the compressor. Ls=0 (mm) (on the abscissa axis)represents the position of the shuttle valve in the state in which theshuttle valve is at the lowermost position or the position in which thespring 62 is most compressed.

In the range from Ls=0 (mm) to Ls=7 (mm), the shuttle valve 60 has movedto various positions so that bypass holes 50 a, 51 a, 50 b, and 51 b areopened sequentially and the capacity of the compressor decreases toabout 50%.

Beyond Ls=7 (mm), bypass hole 52 a opens and when shuttle valve 60reaches the uppermost position [Ls=13 (mm)] wherein the spring 62 isfully extended, the operation will be at about 0% of the capacity.

As has been described earlier, bypass hole 52 a has an independentbypass passage 67 thus preventing back flow of a bypass gas into bypassholes 50 a, 51 a, 50 b and 51 b on the downstream side thereby enablingcapacity control without reducing the control efficiency.

To more fully understand the operation of the scroll compressor of thepresent invention, a description of the operation of shuttle valve 60will be given by using the following symbols:

spring constant of spring 62: k;

initial flection of spring 62: X0;

maximum stroke of shuttle valve 60: X1 (=13 mm); and

cross-sectional area of cylinder 61: Sv.

The forces acting on shuttle valve 60 can be obtained by the followingequations:

The force Fp with which control pressure Pm moves shuttle valve 60downward (against the action of the spring 62 is:

FP=(Pm−Ps)×Sv.

The force Fs with which spring 62 moves shuttle valve 60 upward is:

 Fs=k×(X 0+X 1−Ls).

From the above equations, the spring force Fs0 acting on shuttle valve60 when shuttle valve 60 is at the lowermost position (Ls=0) iscalculated to be:

Fs 0=k×(X 0+X 1).

The spring force Fs1 acting on shuttle valve 60 when shuttle valve 60 isat the uppermost position (Ls=X1) is calculated to be:

Fs 1=k×X 0.

Consequently, at the time of operation at the maximum capacity, Fp≧Fs0,the force exerted on the shuttle valve 60 by the control pressure isgreater that the force exerted by the spring causing the shuttle valve60 to move to the lowermost position. Conversely, at the time ofoperation at the minimum capacity, Fp≦Fs1 allowing the spring 62 to moveshuttle valve 60 to the uppermost position. Also, at the time ofcontrolled capacity operation, Fp=Fs and the shuttle valve 60 isbalanced at an intermediate position.

The pressure characteristics (Pm vs. Ps characteristics) of pressurecontrol valve 70 of the compressor of an exemplary embodiment of thepresent invention are illustrated in FIG. 6. For example, when the highpressure Ph is 15 kgf/cm², the load characteristics of spring 62 aredesigned as below:

Fs 0/Sv=3.0 kgf/cm²,

Fs 1/Sv=0.5 kgf/cm².

When the cooling load is high, the suction pressure Ps rises resultingin a rise in the control pressure Pm. As represented in FIG. 6, when thesuction pressure, Ps is equal to or greater than 1.8 kgf/cm² thedifference between the control pressure and the suction pressure will beequal to or greater than 3 kgf/cm²,

(Pm−Ps≧3 kgf/cm²(=Fs 0/Sv))

resulting in force Fp due to control pressure equaling or exceeding thespring force Fp (Fp≧Fs0), and thus the shuttle valve 60 is pushed downto the lowermost position where the spring 62 is compressed. Thus, thebypass holes 50 a, 51 a, 50 b, 51 b and 52 will be closed causing thecompressor to operate at the maximum capacity increasing the coolingcapacity.

Conversely, when the cooling load is low, the suction pressure Ps dropsresulting in a drop in the control pressure Pm. When the suctionpressure Ps drops to 1.3 kgf/cm² or less the force due to the controlpressure (Fp) is less than or equal to the force from the partiallycompressed spring (Fs1) (Fp≦Fs1) and shuttle valve 60 is pushed up tothe uppermost position (by the force of the spring 62) causing thecompressor to operate at the minimum capacity decreasing the coolingcapacity. The Ps range of 1.8 kgf/cm²<Ps<1.3 kgf/cm² is the range ofcontrolled operation in which the control mechanism can stabilize thesuction pressure Ps at an optimum value for the cooling load.

The pressure control valve 70 of the present invention also reduces thestarting shock. When the compressor stops the high pressure Ph dropsaccompanying a drop in the control pressure Pm resulting in Pm beingnearly equal to Ps. Fp becomes nearly equal to zero kgf/cm² allowing thespring 62 to push shuttle valve 60 upward thereby opening all the bypassholes 50 a, 51 a, 50 b, 51 b and 52 a. Thus, when the operation issubsequently restarted, the compressor starts from the minimum capacitythus relieving the start shock and assuring a smooth start-up.

Industrial Application

As is clear from the above-described exemplary embodiment, thecapacity-controlled scroll compressor of the present invention, has areduced start shock as the high pressure which works as the controlpressure of a shuttle valve for opening and closing bypass holes isintroduced from a high pressure passage opening at a discharge hole.When the compressor stops, the pressure in the area of the dischargehole reduces immediately, thereby reducing the control pressure whichcontrols the movement of the shuttle valve 60. The reduced controlpressure enables the spring 62 to cause the shuttle valve 60 to move tothe uppermost position (i.e., the position where spring 62 is mostextended) opening the bypass holes 50 a, 51 a, 50 b, 51 b and 52 a sothe compressor is generating at the minimum capacity. Once thecompressor starts, the control pressure increases causing the shuttlevalve 60 to compress spring 62 and move towards the lowermost positiongradually increasing the capacity of the compressor.

Also, the present invention enhances manufacture of the compressor byemploying a configuration in which one of the bypass holes 52 a isformed on the side wall of the discharge hole 1 c so that thesimultaneous machining of the bypass hole 52 a and a passage 67 (thatcommunicates with the bypass hole 52 a and the cylinder 61) can beperformed from the outer peripheral end of a fixed end plate. Thus, itis possible to improve the machinability of the fixed end plate.

Furthermore, the compressor of the present invention further employs aconfiguration in which the high pressure passage 72 is coaxial to thelow pressure passage 67 (see FIGS. 1 and 3) so that passages 67, 72 andbypass hole 52 a in the side wall of the discharge hole 1 c can besimultaneously machined from cut out 1 h in the outer peripheral end ofthe fixed end plate.

Thus, the present invention provides an improved variable capacityscroll compressor that incorporates control structure in the fixed endplate which makes it possible to reduce the start shock while providinga compressor having a fixed end plate with superior machinability.

The present invention has been shown and described in what is consideredto be the most practical and preferred embodiment. It is anticipated,however, that departures may be made therefrom and that obviousmodifications will occur to persons skilled in the art.

We claim:
 1. In a capacity-controlled scroll compressor comprising; acompressor housing; a fixed scroll having a fixed end plate and a spiralwrap extending from said fixed end plate; an orbiting scroll having anorbiting end plate and a spiral wrap extending from said orbiting endplate and disposed in engagement with said fixed scroll with respectivewraps facing each other; said wraps of said fixed scroll and saidorbiting scroll intermeshed to define a plurality of fluid compressionpockets and positioned to receive fluid to be compressed from a suctionchamber in said housing, said fixed scroll and said orbiting scrollbeing disposed inside of said compressor housing; an orbiting mechanismformed on the rear side of said orbiting end plate opposite the spiralwrap of said orbiting scroll; a drive shaft rotatably supported in saidcompressor housing with the main shaft portion thereof projecting tooutside of said compressor housing passing through a shaft sealingdevice and a subsidiary bearing through a main bearing; a drivetransmission mechanism for transmitting the driving force from saiddrive shaft to said orbiting mechanism; a rotation restraining componentfor restraining rotation of said orbiting scroll as to make it orbit; arevolution restraining component adjacent to said rotation restrainingcomponent for restraining the direction of motion of said rotationrestraining component to the direction at right angles to said driveshaft; a discharge port formed in said fixed end plate communicatingwith the fluid compression pocket near the end of its formation; and adischarge valve at the end of said discharge port; an improved capacitycontrol mechanism comprising: at least a pair of bypass holes in saidfixed end plate communicating with a pair of fluid compression pocketsformed in between both wraps at positions substantially symmetrical withrespect to said fixed end plate; a cylinder formed inside said fixed endplate in a manner communicating with said pairs of fluid pockets throughsaid bypass holes; a shuttle valve inside said cylinder mounted forreciprocal motion therein to vary the opening of said bypass holes tochange the capacity of said compressor; a spring in said cylinderopposing reciprocation of said shuttle valve; a fixed end plate furtherincluding a control-pressure chamber housing a pressure control valvefor generating a control pressure for causing the reciprocation of saidshuttle valve against said spring responsive to said control pressure;and a high pressure passage in said fixed end plate between saidcontrol-pressure chamber and said discharge port of said fixed end platelocated before said discharge valve for introducing said compressedfluid at relatively high pressure to said pressure control valve whereinsaid pressure control valve generates a control pressure from saidrelatively high pressure fluid responsive to pressure in said compressorhousing.
 2. The capacity-controlled scroll compressor of claim 1,further including a bypass hole formed on the side wall of the dischargeport and a passage between said bypass hole and said cylinder, wherebysaid compressed fluid at relatively high pressure is directed to saidshuttle valve through said passage and the reciprocation of said shuttlevalve responsive to said control pressure selectively varies the outputof said compressor.
 3. The capacity-controlled scroll compressor ofclaim 2, wherein said passage between said bypass hole and said shuttlevalve is substantially coaxial with said bypass hole on the sidewall ofsaid discharge port.
 4. The capacity-controlled scroll compressor ofclaim 3, wherein said fixed end plate further includes a low pressurepassage communicating with said cylinder and providing a passageway fromsaid cylinder to the outer peripheral surface of said fixed end plate.5. The capacity-controlled scroll compressor of claim 4, wherein saidlow pressure passage is coaxial with said passage between said bypasshole in said cylinder.
 6. The capacity-controlled scroll compressor ofclaim 5, wherein said low pressure passage, said bypass hole and saidpassage between said bypass hole and said cylinder are coaxial andaccessible from said outer peripheral surface of said fixed end plate.7. The capacity-controlled scroll compressor of claim 2, wherein said atleast a pair of bypass holes and said bypass hole formed on the sidewallof the discharge port selectively communicate with the low pressure areaof said compressor through separate passages responsive to said controlpressure.
 8. In a capacity-controlled scroll compressor comprising: acompressor housing; a fixed scroll having a fixed end plate and a spiralwrap extending from said fixed end plate; an orbiting scroll having anorbiting end plate and a spiral wrap extending from said orbiting endplate and disposed in engagement with said fixed scroll with respectivewraps facing each other; said wraps of said fixed scroll and saidorbiting scroll intermeshed to define a plurality of fluid compressionpockets and positioned to receive fluid to be compressed from a suctionchamber in said housing, said fixed scroll and said orbiting scrollbeing disposed inside of said compressor housing; an orbiting mechanismformed on the rear side of said orbiting end plate opposite the spiralwrap of said orbiting scroll; a drive shaft rotatably supported in saidcompressor housing with the main shaft portion thereof projecting tooutside of said compressor housing passing through a shaft sealingdevice and a subsidiary bearing through a main bearing; a drivetransmission mechanism for transmitting the driving force from saiddrive shaft to said orbiting mechanism; a rotation restraining componentfor restraining rotation of said orbiting scroll as to make it orbit; arevolution restraining component adjacent to said rotation restrainingcomponent for restraining the direction of motion of said rotationrestraining component to the direction at right angles to said driveshaft; a discharge port formed in said fixed end plate communicatingwith the fluid compression pocket near the end of its formation; and adischarge valve at the end of said discharge port; an improved capacitycontrol mechanism comprising: at least a pair of bypass holes in saidfixed end plate communicating with a pair of fluid compression pocketsformed in between both wraps at positions substantially symmetrical withrespect to said fixed end plate; a cylinder formed inside said fixed endplate in a manner communicating with said pairs of fluid pockets throughsaid bypass holes; a shuttle valve inside said cylinder mounted forreciprocal motion therein to vary the opening of said bypass holes tochange the capacity of said compressor; a spring in said cylinderopposing reciprocation of said shuttle valve; a fixed end plate furtherincluding a control-pressure chamber housing a pressure control valvefor generating a control pressure for causing the reciprocation of saidshuttle valve against said spring responsive to said control pressure; ahigh pressure passage in said fixed end plate between saidcontrol-pressure chamber and said discharge port of said fixed end platelocated before said discharge valve for introducing said compressedfluid at high pressure to said pressure control valve wherein saidpressure control valve generates a control pressure from said highpressure fluid responsive to pressure in said compressor housing; abypass hole formed on the side wall of said discharge port and a passagebetween said bypass hole and said cylinder wherein said high pressurefluid is directed to said shuttle valve through said passage; and a lowpressure passage communicating with said cylinder and providing apassageway from said shuttle valve to the outer peripheral surface ofsaid fixed end plate wherein said bypass hole, said passage between saidbypass hole and said cylinder and said low pressure passage aresubstantially axially aligned and accessible from said outer peripheralsurface of said fixed end plate.